This is a very common practice, especially with those businesses that deal with clients mostly off line, such as retailers or dentists. When a new customer walks in to your shop or practice, you can ask him to sign up for your email newsletter. You then enter that information to your database, and then regularly upload the new information to your ESP account.
Uploading these new subscribers shouldn’t be a problem, however, you may run into difficulties updating email addresses of your existing clients who are already receiving your ezine. Ideally, your subscribers should update their own information on line, using your ESP’s forms and tools (that’s one of the reasons you pay that monthly fee, right?). However, sometimes, customers feel more comfortable giving you their new email address over the phone, or more likely, in person, while they are making another purchase, or visiting your place of business.
The problem here lies in the fact that most ESPs track your subscribers by their email address, not their name, or some other identifier. Because of this, updating an email address of an existing subscriber may be tricky.
If you’re using 1ShoppingCart, Aweber or GetResponse, uploading a list containing new email addresses will trigger a “confirmation email” to be sent to those new subscribers.
Since you’re only updating existing subscribers’ data, you will have to do it by hand, one by one by manually searching for the subscribers whose address needs updating and then entering the new address directly.
However, if you’re using Constant Contact, and you have double opt-in turned off, you can upload your “new” and existing subscribers. If you accidentally upload some of the old subscribers who have opted out on line, that’s not going to be a problem since Constant Contact maintains a Do Not Mail list, and those addresses will not be added to your list.